Can God accept my prayer to return my fiancée to me after my sincere repentance, or is what happened a divine punishment for my return to sins?

Repentance involves abandoning the sin, regretting it, and resolving not to return to it. It is accepted even if the sin is repeated and repentance is repeated, because Allah says: "Indeed, Allah loves those who repent and loves those who purify themselves," and because the Prophet, peace and blessings be upon him, said: "I have forgiven My servant three times, so let him do as he wills." So, if you repent with sincere repentance, the sins you repented from will not be a cause for Allah to punish you. The soundness of repentance does not necessarily mean the return of your fiancée. Rather, entrust your affairs to Allah and strive in repentance and righteous deeds. Remember that sincere repentance is purely for the sake of Allah, out of hope and fear, and not for worldly gains.